The issue of State secession was first considered by the Hartford Convention during the closing days of the War of 1812. As far as I know, though they were eventually persuaded to abandon their plan, they weren’t forbidden to secede by any law. (Does any such law yet exist?)
The Confederacy was kept in the Union by military force, so probably, the feuderal government could still prevent secession by force, though economic wherewithal for protracted battle might be hard to come by, if conditions deteriorate to the extent that secession seems better than remaining.
Still, no denial of future exit was ever imposed as a condition of statehood. Would you join an organization which had as condition of membership, that regardless of how the organization might later treat you, you could nonetheless, never leave? Too much like “Hotel California” for me.
So, if over the next 20 years, this betrayed and crumbling Republic becomes a perfect “Peoples’ Republic”, but remains territorially intact, would you conclude that it had “survived?”